Steering Yoke

ABSTRACT

A yoke for use in a rack and pinion steering assembly is described. The yoke may include a bearing surface that provides a low coefficient of friction, allowing for a greater biasing force against the rack shaft. The materials and design of the yoke can provide for a quieter system with reduced vibration.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/074,413 filed on Jun. 20, 2008. This applicationalso claims the benefit of U.S. Provisional Patent Application Ser. No.61/081,816 filed on Jul. 18, 2008. These applications are hereby fullyincorporated herein by reference.

BACKGROUND

1. Field of Invention

The invention relates to bearings and, in particular, to steering yokebearings and bearing assemblies.

2. Discussion of Related Art

Many vehicles use rack and pinion steering gear to translate motion fromthe steering wheel to the turning wheels on the road. In these systems,the steering wheel is joined to a pinion gear that includes gear teeththat are mated with teeth on a rack shaft. As the pinion gear rotates,the motion is translated into linear motion of the rack shaft that isconnected to tie rods. The tie rods then rotate the turning wheels tocause the vehicle to turn. To assure proper lash between the pinion andthe rack shaft a steering yoke assembly may be used to provide a biasingforce that forces the shaft into the pinion gear. The yoke may also bereferred to as a “yoke assembly,” “yoke slipper,” or “puck.” The rackshaft (typically steel) slides along the yoke when the pinion gear isrotated. Friction between the shaft and the yoke can be minimized byusing a low friction bearing on the contact surface of the yoke. Otherfriction reducing methods include the use of rolling elements (balls)and the addition of lubricants such as grease. These steering systemsmay be mechanical, hydraulic or electric.

SUMMARY

Disclosed herein are a variety of devices and methods directed to themanufacture and use of a steering yoke that may be useful inapplications such as rack and pinion steering assemblies. The steeringyoke may be hollow and can include a circular groove designed tocomplement and support a steering rack shaft. The groove may include alow friction coating that can be formed from a polymer. The yoke mayalso include a spring perch constructed and arranged to seat a springthat provides a biasing force to the steering yoke bearing.

In one aspect a steering yoke is provided, the steering yoke comprisinga hollow cylinder including an first end and a second end, the first enddefining at least one of: an arcuate indent for receiving a steeringrack shaft wherein the arcuate indent includes a contact surfacecomprising a low friction polymer layer; and a spring perch constructedand arranged to support and retain a spring for supplying a biasingforce to the yoke.

In another aspect a method of forming a steering yoke body is provided,the method comprising the steps of drawing a metal/polymer laminate overa die to produce a substantially hollow form having a top surface and anopen bottom, and forming in the top surface at least one of: a concavearcuate groove shaped to complement a steering rack shaft; and a springperch constructed and arranged to support a spring for supplying abiasing force to the yoke body.

In another aspect, a method of forming a steering yoke body is provided,the method comprising the steps of rolling a metallic sheet into acylinder, affixing the adjoining edges of the sheet to each other, andattaching a concave arcuate bearing surface to one end of the cylinder,the bearing surface constructed and arranged to receive a steering rackshaft.

The subject matter of this application may involve, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of a single system or article.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is an exploded diagram of a rack and pinion steering system;

FIG. 2 is a cutaway view of a portion of a rack and pinion steeringsystem;

FIG. 3A is a perspective view of an embodiment of a drawn steering yoke;

FIG. 3B is a perspective view of one step in the production of oneembodiment of a drawn steering yoke;

FIG. 3C is a perspective view of another step in the production of theembodiment shown in FIG. 3B;

FIG. 3D is an embodiment related to the embodiment of FIG. 3A;

FIG. 4 is a perspective view of another embodiment of a steering yoke;

FIG. 4B is an embodiment similar to that shown in FIG. 4A.

FIG. 5 is a perspective view of another embodiment of a steering yoke;

FIGS. 6A and 6B provide a perspective view of another embodiment of asteering yoke.

FIG. 7 provides graphical test results for various steering yokeembodiments; and

FIG. 8 is a bar graph showing Coefficient of Friction data for variousembodiments.

DETAILED DESCRIPTION

In one aspect a steering yoke and steering yoke assembly are describedin which the bearing contact surface of the yoke exhibits reducedfriction that allows for a greater biasing force against the rack shaft.This increased biasing force can result in reduced noise and vibrationin the steering column. Lower friction levels can also enable the use oflower levels of power assistance enabling the use of electric motors orelectric powered hydraulic pumps. In many cases it can be important tohave substantially low, consistent coefficients of friction over thelife of the yoke bearing and yoke assembly.

In another aspect, reduced noise and vibration in a steering system canbe realized through the use of a substantially hollow yoke assembly.When compared to cast, machined or injection molded yoke assemblies, asubstantially hollow yoke may reduce vibration. Hollow yokes (“cans”)can be produced by forming the can from a sheet or by drawing a sheet ofmaterial over a die in one or more steps. The sheet material may be alaminate of a metal and a polymer. A “hollow yoke” is a yoke that issubstantially hollow rather than solid throughout the yoke body. Thehollow yoke has an interior cavity that may be empty or may be filledwith another material. In various embodiments the bearing may be usedwith or without grease.

An exploded view of a typical steering assembly 10 is provided inFIG. 1. Helical pinion gear 110 is mated with teeth on a rack shaft (notshown in FIG. 1). Yoke assembly 120 is inserted into pinion housing 130and provides a biasing force that causes the rack shaft to maintainproper lash with the pinion gear 110. The system is typically lubricatedwith a grease such as a lithium grease. FIG. 2 provides a cutaway viewof a portion of the steering mechanism of FIG. 1. Helical pinion gear110 is mated with rack shaft 122 which maintains mechanical contact withthe aid of steering yoke 140. Steering yoke 140 is pressured againstpinion gear 110 by spring 160. Spring 160 is compressed and retained bythreaded cap 166. 0-ring 162 is seated in a channel that circumscribesyoke 140. The O-ring may also be seated in a groove that circumscribesthe inner surface of housing 130. When an operator turns the steeringwheel of the vehicle, pinion gear 110 rotates causing rack shaft 122 toslide either in or out of the page as configured in FIG. 2. The rackshaft 122 slides against a stationary yoke 140 which maintains a biasingforce that keeps the gear and shaft meshed together. A stronger biasingforce can help to achieve a less noisy steering mechanism, however, if astronger force is provided by spring 160 a greater amount of frictionand resulting wear will occur between yoke 140 and rack shaft 122.

Existing steering yokes are typically made from die cast metal orinjection molded plastic to which a low friction liner is attached. Ithas been found that these solid materials can transmit vibration andnoise resulting in undesirable vibrations in the steering mechanism.This system noise and vibration may worsen as the yoke ages and istypically detected at the steering wheel through “driver feel.” Some ofthe yokes described herein employ a hollow body design that surprisinglyresults in a reduction in the transmission of noise and vibration. Ahollow yoke can also reduce the weight of the steering mechanism.

A steering mechanism can be exposed to a wide range of temperatures thatmay be the result of, for example, environmental temperature shifts ortemperature increases due to work and/or friction. As steering yokes aretypically made of different material than the housing (often aluminum)in which they are encased there may be tolerances built into the yokethat allow for thermal expansion and contraction of the yoke in thehousing. But these tolerances can also result in excessive clearancebetween the yoke and the shaft and the housing. This excessive clearancecan result in additional noise in the system. Having determined one ofthe causes of this excessive noise, a hollow aluminum yoke havingsimilar or identical thermal expansion characteristics can be made totighter tolerances and can reduce the amount of play, providing aquieter steering mechanism with reduced vibration.

A hollow yoke may be constructed in a number of ways. For instance, theyoke may be extruded, formed, molded, pressed, rolled, machined, or anycombination of these processes. In one set of embodiments, a metal ormetal/polymer sheet is transformed into a yoke. For example, a hollowyoke can be constructed by drawing a stamped metal sheet ormetal/fluoropolymer laminate over a die. Alternatively, a low frictionlayer, such as an acetal resin, may be mechanically attached to thebearing surface. Additional steps may be used to form a concave arcuateportion at one end that is constructed and arranged to support asteering rack shaft. The arcuate portion may be a partial cylinder asshown in FIG. 3A. In cases where the drawn material does not include afluoropolymer, a lubricious bearing surface can be attached to the yokebody by, for example, a boss (FIG. 5), a press fit, or an adhesive. Ahollow yoke may also be produced by wrapping a sheet of metal ormetal/fluoropolymer laminate into a three dimensional shape that may becylindrical or substantially cylindrical. The edges may be joined by,for example, welding. A hollow yoke may include a cylinder wall that hasa thickness of less than 5 mm, less than 2 mm, less than 1 mm or lessthan 0.5 mm. An end cap may be added in a separate step and may be of asimilar or dissimilar material. A polymeric bearing surface, such as anacetal resin or a fluoropolymer, may also be added to the end cap. Ifthe can is produced from a metallic sheet, a fluoropolymer layer may beattached to the outer metal surface by mechanical or adhesive means.

In one aspect of the invention, a portion of the yoke that does notcontact the rack shaft may include a polymer layer. This portion may be,for example, the exterior surface of the walls of the cylindricalportion as shown in FIGS. 3A-3C. This may be in addition to theinclusion of a polymeric layer on arcuate surface 224 which supports areciprocating shaft. Cylinder wall 226 may not be in contact with thereciprocating steering shaft but can also include a polymer (e.g.,fluoropolymer) layer. It has been learned that a fluoropolymer layer oncylinder wall 226 can provide for a quieter, more secure fit in a yokehousing. In addition, manufacturing tolerances can be eased as a solidfluoropolymer may “cold flow,” allowing the yoke to be pressed into ahousing that would be too tight to accept the yoke if it comprised onlyan aluminum or steel cylinder wall fitted into a steel or aluminumhousing. This feature can also minimize noise and vibration as the yokecan be inserted into the housing with zero clearance. One result can beimproved feel at the steering wheel throughout the life of the steeringmechanism.

In one set of embodiments, the contact surface of the yoke may comprisea polymer such as a laminate of a fluoropolymer over a metal substrate.The fluoropolymer may be adhered to the substrate by, for example,mechanical adhesion or lamination with a fluoropolymer hot meltadhesive. The fluoropolymer may be, for example, PTFE, and the metal maybe, for example, aluminum, steel, bronze, copper or alloys thereof. Thelaminate may be free of lead. The polymer may include one or morefillers such as graphite, glass, aromatic polyester (EKONOL®), bronze,zinc, boron nitride, carbon and/or polyimide. One embodiment includesboth graphite and polyester fillers. Concentrations of each of thesefillers in a polymer such as PTFE may be greater than 1%, greater than5%, greater than 10%, greater than 20% or greater than 25% by weight.Additional layers, such as a bronze mesh between the metal and thefluoropolymer, or embedded in the fluoropolymer, may also be used. Suchmaterials include the NORGLIDE® line of products available fromSaint-Gobain Performance Plastics Inc. Suitable examples of NORGLIDEproducts include NORGLIDE PRO, M, SM, T and SMTL. The thickness of thefluoropolymer layer may vary or be constant across the substrate. Thefluoropolymer layer may have an average thickness in the contact zone ofgreater than or equal to 30 μm, 50 μm, 75 μm, 100 μm, 150 μm, 200 μm, or250 μm. Thicker fluoropolymer layers have been shown to provide a moreconsistent bearing load over the life of the yoke. In some embodiments,the metal substrate may have a nominal thickness of, for example, from100 μm to 5 mm. More specific ranges include 200 μm to 4 mm for aluminumand 200 μm to 1.23 mm for steel.

The contact surface of the yoke may be textured so that some portions ofthe surface are higher than other portions. Texturing may include aplurality of peaks and valleys. The peaks may measure greater than orequal to 10 μm, 20 μm, 50 μm, 100 μm or 200 μm above the adjacentvalley. The texturing of the surface can provide numerous reservoirs forretaining grease. The texture may be patterned or random and can beconsistent across the contact surface. In one embodiment, a patternedtextured surface may be formed by depositing a fluorocarbon layer over ascreen, such as a bronze mesh. When assembled, the smooth surface of thesteel rack shaft may contact the yoke at numerous high points, or peaks,across the contact surface. Contact points may be distributed across thesurface so that the force between the yoke and the rack shaft is born bya large portion of the arcuate region. For example, the contact pointsmay be found on more than 50%, more than 70%, more than 80% or more than90% of the arcuate surface region. The force may be substantiallyequally distributed between central and edge portions of the arcuateregion. Thus, the pressure exerted by the yoke against the cylindricalrack shaft may be substantially equivalent across the width and lengthof the bearing surface. This is in contrast to alternative designs,e.g., gothic arches, in which two distinct lines of contact are providedbetween the rack shaft and the bearing surface. In a “gothic arch”design, the surface of the bearing is constructed with an offset radiusto promote two regions of contact with the rack shaft. These linearregions typically run parallel to the axis of the rack shaft and may be,for example, at 45 degrees from the center of the shaft. This design isbelieved to reduce drag between the bearing surface and the rack shaft.As the bearing surface is worn in, the area of these two linear regionsmay expand until the entire bearing surface is in contact with the rackshaft. This additional surface area contact contributes to a highercoefficient of friction that has been measured in worn bearings. Thus,due to the change in contact area over time a gothic arch design yokemay exhibit a much lower coefficient of friction when new than after100,000 or 200,000 cycles.

In one set of embodiments, a bearing surface is shaped to contact therack shaft with equal force at the central and peripheral portions ofthe bearing surface. This may allow for a greater biasing force to beapplied to the yoke and shaft, resulting in a quieter mechanism.Although such a design has historically been considered to provide toomuch friction for this application, it has been found that by using thebearing surfaces described herein that the coefficient of friction (COF)can be as low as or lower than with gothic arch designs. Bearingsurfaces can incorporate this design in new, unused bearings and thearea of contact between the rack shaft and the low COF polymer willremain substantially constant over the life of the bearing. This is incontrast to the increasing COF that has been found over the lifetime ofconventionally designed bearings that do not initially provide contactacross a majority of the bearing surface.

In most steering yoke designs, the bearing surface is biased against therack shaft by a spring (in compression), such as spring 160 as shown inFIG. 2. The bearing load at the bearing/shaft interface typicallychanges as the bearing surface wears because as the spring expands toretain contact between the worn bearing surface of the yoke and the rackshaft, the force applied by the spring decreases. Therefore, wear in thebearing surface is typically accompanied by a corresponding drop inbearing load. This drop in load can result in, for example, undesirablenoise and vibration. It has been found that bearing surfaces includingfluoropolymer layers of greater than 100 μm can result in a consistentbearing load over 100,000 or 200,000 cycles.

FIG. 3A provides a perspective view of one embodiment of a steering yokeassembly. Hollow yoke 222 includes an open bottom (not shown), asubstantially cylindrical wall 226 and an arcuate upper surface 224 thathas a radius of curvature that is substantially equivalent to that ofthe rack shaft with which the yoke is designed to interface with. Thearcuate depression in the surface may be a groove that has a circularradius and exhibits a partially circular cross-section. The groove maycomplement a cylindrical steering rack shaft and a majority of thesurface of the groove may be in contact with the steering rack shaftwhen a biasing force is applied. The hollow yoke 222 may be a drawn canthat may include a cylindrical or other shaped wall Spring perch 228 canbe attached to yoke 222 via threads, press fitting, welding or analternative connector. A spring (not shown in FIG. 3) similar to thatshown in FIG. 2 can be positioned against spring perch 228 to provide abiasing force to the yoke 222. The perch can provide a substantiallyplanar surface that helps to equalize the spring force across thecontact surface of the yoke. Yoke 222 may be formed by drawing alaminate sheet into the shape shown. The drawing process may include oneor more shaping steps and may include the use of one, two or more dies.For instance a stamped, round sheet may be drawn into the can shapeshown in FIG. 3B. In a subsequent step, the contact surface may beindented to form a concave arcuate surface as shown in FIG. 3C. The dieused to form the concave arcuate feature may have a radius substantiallyequivalent to that of the rack shaft that the yoke is designed tointerface with. FIG. 3C provides an example of a yoke drawn from alaminate of PTFE/EKONOL on aluminum. The yoke shape of FIG. 3C alsoexhibits a surprisingly high compression strength allowing it towithstand forces equal to or greater than those to which solid yokes aretypically exposed in rack and pinion steering systems.

FIG. 3D illustrates a steering yoke assembly with an integral springpocket 228 a. An integral spring pocket is a spring pocket that isformed when the yoke itself is shaped. For instance, the yoke and springpocket may be formed from the same blank. The inclusion of integralspring pocket 228 a can eliminate the need for the addition of aseparate spring perch as in FIG. 3A. In one embodiment, spring pocket228 a can be produced by drawing a blank (that includes portion 228 a ina pre-formed state) over a die to produce the hollow can shown in FIG.3D. The concave portion of spring pocket 228 a can be formed in a secondoperation using a second die or in the same step by using two opposeddies. In this embodiment, bearing surface 224 can be attached to theyoke assembly after the can has been drawn. Spring pocket 228 a includesa concave indent for receiving a spring that can provide a biasing forcethat is transmitted through the yoke to the rack shaft. Spring pocket228 a may include orifice 229. The surface of spring pocket 228 a may bemetallic or include a polymer layer such as a fluoropolymer layer.

FIG. 4A illustrates another embodiment wherein the contact surface 324can be stamped and folded to form an arcuate, partially cylindricalsurface. Contact surface 324 may be cut from a planar sheet such as ametallic sheet or laminate using a stamping die and may then be foldedor bent around a cylinder having the same radius as that of the intendedrack shaft. This piece may then be attached, e.g., by welding, tocylindrical base 326 to from yoke 322. Base 326 may be of metal, plasticor other material but need not be PTFE as it does not contact a movingpart. Spring perch 328, as above, can be used to provide a flat surfaceto transmit the spring force to the yoke.

As shown in FIG. 4B a stamped and folded yoke similar to that shown inFIG. 4A may include an integral spring pocket 328 a. A blank can bestamped from a metallic or metal/polymer composite sheet and the blankmay include portions that, when folded, form spring pocket 328 a. Theblank may be folded and joined at seam 330. Seam 330 may be welded orotherwise joined together to secure the shape of the yoke. The integralspring pocket can eliminate the need for adding separate spring perch328.

FIG. 5 illustrates another embodiment in which base 426 may be formedfrom metal or plastic using molding or drawing techniques. The baseincludes upper surface 430 which defines receiving hole 432. Separatebearing surface 424 may include a polymer, polymer/metal laminate,fluoropolymer or fluoropolymer/metal laminate as described herein.Bearing surface 424 may include boss 434 which is sized to be press fitin receiver 432. Thus contact surface 424 may be press fit into the yokebody 426 to produce a yoke that includes an arcuate, low-friction,contact surface. Spring perch 428 operates as previously described.

FIGS. 6A and 6B provide an illustration of a steering yoke produced byrolling or wrapping a metal or metal/polymer sheet around a cylindricalmandrill. Hollow cylindrical body 526 may be formed by first stamping aflat from a metallic or laminate sheet. The flat may then be rolledaround a mandrill of appropriate diameter to produce a hollowcylindrical body 526 that is open at both the bottom and top. The edgesof cylindrical body may be permanently joined by, for instance, welding.Cylindrical body 526 may optionally include a polymeric coating on theouter surface. Bearing surface 524 may be fabricated separately fromcylindrical body 526 and can include a polymeric surface layer that maybe textured, as shown. The texture features can provide lubricantreservoirs while still providing contact and support for a steering rackshaft (not shown) across a majority of the arcuate bearing surface. Forinstance, when biased (by a spring, for example) against a steering rackshaft, edge portion 532 may be subjected to approximately the samepressure against the shaft as is central portion 534. The polymericcoating on bearing surface 524 may be attached to a metallic substrate(e.g., steel or aluminum) by an adhesive or by mechanical bonding, forexample. The bearing surface may be formed directly from a laminate orthe polymer coating can be attached after the bearing surface is formed.Appropriate polymers may include fluoropolymers and acetal resins andmay contain fillers such as graphite or EKONOL. Bearing surface 524 canbe permanently attached to cylindrical body 526 by, for example,welding. A mesh screen, such as a bronze mesh screen, may be positionedin or adjacent to the polymer coating.

As shown in FIG. 6A spring perch 528 may be separately formed and may beattached to cylindrical body 526 by welds 542 a, 542 b, etc. Circularindent 544 can help to retain a spring (not shown) in compression thatis kept centered by upwardly projecting dimple 546. Spring perch 528 maybe designed to transmit the force provided by the spring equally acrossopposed bearing surface 524 which can be in contact with a steering rackshaft (not shown). Spring perch 528 may be metallic and in someembodiments can be made of steel or aluminum. It can be formed by, forexample, stamping a circular flat with a die of appropriate shape anddimensions.

To evaluate different yoke bearing designs, a test was formulated inwhich different bearing formulations were used in similarly designedbearing structures. Each of the bearing surfaces was subjected to a testin which an initial load of 2935 N was applied for 200,000 cycles at afrequency of 1 Hz and a stroke of ±90 mm. Each yoke bearing wasmonitored for 1) change in load; 2) wear; and 3) friction. Each bearingsurface was manufactured separately from the yoke and included a gothicarch design. Bearing material A1 was made from NORGLIDE EKO15, a PTFEmaterial including 15% EKONOL and 5% graphite on a steel backingsubstrate. Bearing material A2 was a duplicate of A1. Bearing material Bwas made from NORGLIDE SMTL1.0T which is a PTFE material containing 25%EKONOL, and no graphite, on a steel substrate. Bearing C was made from aDX material (Garlock Bearings LLC) that includes a 250 μm layer ofacetyl resin over a 250 μm layer of sintered bronze on a steel backing.Bearing D was made from a DU material from Garlock Bearings LLC thatincludes lead and bronze in a PTFE layer on a steel backing. Each of thetested bearings was lubricated with Shell Alvania Extreme Pressure IIlithium grease.

The graph provided in FIG. 7 illustrates the bearing load and the wearlevel for each of the tested bearing surfaces. The results indicate thatthe NORGLIDE bearing surfaces provided a more consistent bearing loadand reduced wear when compared to the DX material. Results showed thatmaterials A and B performed comparably to the DU material. FIG. 8provides coefficients of friction for each of the bearing materials whennew, after 100,000 cycles, and after 200,000 cycles. Coefficients offriction were measured using a friction load cell. The NORGLIDE surfaces(A and B) actually resulted in a decrease in (although substantially thesame) coefficient of friction with additional cycles. A value for thecoefficient of friction is considered to be substantially the same as asecond value if it is within 50% of the second value. In someembodiments, the change in coefficient of friction after use may be lessthan 25% or less than 10% of the original value. The DU and DX materialsshow significantly increased levels of friction with increasing cycles.To maintain consistent performance in a steering mechanism, a yoke thatincludes a bearing surface that retains a consistently low level offriction may be preferred. Thus, these results indicate that either ofthe NORGLIDE materials can provide a superior bearing surface for asteering yoke when compared to the DX or DU material. Examination ofeach of the bearing surfaces was also instructive. The DU materialshowed significant wear down to the bronze layer after 100,000 cycles,and the PTFE layer had been completely removed. Materials A and B(NORGLIDE) showed little wear and maintained an intact layer of PTFEacross the bearing surface. This can result in a superior combination ofconsistent bearing load and consistently low coefficient of frictionover 200,000 cycles which can provide for a longer product lifetime.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified, unless clearly indicated to the contrary.

All references, patents and patent applications and publications thatare cited or referred to in this application are incorporated in theirentirety herein by reference.

1. A steering yoke comprising: a hollow cylinder including an first endand a second end, the first end defining at least one of: a) an arcuateindent for receiving a steering rack shaft wherein the arcuate indentincludes a contact surface comprising a low friction polymer layer; andb) a spring perch constructed and arranged to support and retain aspring for supplying a biasing force to the yoke.
 2. The steering yokeof claim 1 wherein the yoke includes a cylindrical wall having an innersurface and an outer surface, the outer surface of the cylindrical wallincluding a low friction polymer layer.
 3. The steering yoke of claim 2wherein the cylindrical wall comprises steel or aluminum.
 4. Thesteering yoke of claim 1 wherein the polymer layer on the contactsurface contains one or more fillers selected from an aromatic polyesterand graphite.
 5. The steering yoke of claim 1 wherein the contactsurface comprises a bronze mesh screen.
 6. The steering yoke of claim 1wherein the polymer layer on the contact surface comprises afluoropolymer or acetal resin.
 7. The steering yoke of claim 1 whereinthe polymer layer has a nominal thickness of greater than 50 μm.
 8. Thesteering yoke of claim 1 wherein the polymer layer has a nominalthickness of greater than or equal to 100 μm.
 9. An assembly comprisinga housing, a spring and the steering yoke of claim
 1. 10. The steeringyoke of claim 1 comprising an integral spring perch on either the firstor second end and an arcuate indent on the opposed end, the arcuateindent comprising a polymer layer on its outer surface.
 11. The steeringyoke of claim 1 wherein the first end of the hollow cylinder includesthe arcuate indent for receiving a steering rack and wherein the arcuateindent is a groove dimensioned to support a steering rack shaft, theexposed surface of the groove comprising a low friction polymer layerwherein the groove surface includes a central portion and two lateraledge portions, the groove constructed and arranged to support a steeringrack shaft with equivalent force per area at the central portion and twolateral edge portions.
 12. The steering yoke body of claim 11 whereinthe groove surface is textured with peaks and valleys and the peakheight averages at least 10 μm. 13-17. (canceled)
 18. The steering yokebody of claim 11 wherein the contact surface is essentially lead free.19. The steering yoke body of claim 11 wherein the body exhibitssubstantially the same coefficient of friction with a steel rack shaftafter 100,000 cycles.
 20. The steering yoke body of claim 11 wherein thegroove is constructed and arranged to support and contact a steeringrack shaft across substantially the entire groove surface. 21-23.(canceled)
 24. A method of forming a steering yoke body comprising:rolling a metallic sheet into a cylinder; affixing the adjoining edgesof the sheet to each other; and attaching a concave arcuate bearingsurface to one end of the cylinder, the bearing surface constructed andarranged to receive a steering rack shaft.
 25. The method of claim 24wherein the metallic sheet includes a low friction polymer layer. 26.(canceled)
 27. The method of claim 24 wherein the bearing surfaceincludes a low friction layer.
 28. The method of claim 24 furthercomprising fixing a low friction layer to the bearing surface usingeither mechanical bonding or an adhesive.
 29. The method of claim 24wherein the metallic sheet includes one or more integral portions thatform an integral spring pocket.
 30. The method of claim 27 wherein thelow friction layer comprises a fluoropolymer and/or an acetal resin.